Thixotropic polyurethane composition

ABSTRACT

The thixotropic polyurethane composition comprises: a liquid of a polyurethane prepolymer having at least two terminal free isocyanate groups and a block polyether compound having at least two terminal secondary alcohol groups. The block polyether compound is a reaction product obtained by addition polymerization of ethylene oxide and propylene oxide in a block form to a starting material having two or three terminal active hydrogen groups in such a polymerization degree that said block polyether compound includes 30 to 409 moles of ethylene oxide and 3 to 172 moles of propylene oxide per molecule and the molar ratio between ethylene oxide and propylene oxide is within the range of 1 : 0.05 to 1 : 0.5. The thixotropic polyurethane composition may further include an inorganic material for enhancing the thixotropic property.

United States Patent 1 Harada et al.

[4 Dec.2,1975

l l TI-IIXOTROPIC POLYURETHANE COMPOSITION [75] Inventors: Hideo Harada; Akinobu Ichihara;

Yasuro Ohmori, all of Kyoto, Japan [73] Assignee: Dai-Ichi Kogyo Seiyaku Co., Ltd.,

Kyoto, Japan [22] Filed: Jan. 29, 1974 I21] Appl. No.: 437,686

[52] US. Cl ..260/77.5 AP; 260/37 N; 260/775 AQ;260/77.5 AM

[51] Int. Cl. C08G 18/32 [58] Field of Search 260/775 AP, 77.5 AQ, 260/775 AM [56] References Cited UNITED STATES PATENTS 4/1968 Lowe et al 260/775 AP OTHER PUBLICATIONS Saunders et al., Polyurethanes, Part II, lnterscience, N.Y., I964, pp. 532 and 534.

Primary Examiner-M. J. Welsh Attorney, Agent, or FirmArmstrong, Nikaido & Wegner [57] ABSTRACT The thixotropic polyurethane composition comprises:

' terminal active hydrogen groups in such a polymerization degree that said block polyether compound includes 30 to 409 moles of ethylene oxide and 3 to 172 moles of propylene oxide per molecule and the molar ratio between ethylene oxide and propylene oxide is within the range of l 0.05 to I 0.5. The thixotropicpolyurethane composition may further include an inorganic material for enhancing the thixotropic property.

11 Claims, N0 Drawings THIXOTROPIC POLYURETHANE COMPOSITION BACKGROUND OF THE INVENTION This invention relates to improved polyurethane compositions and more particularly to thixotropic polyurethane compositions. This invention also relates to a method for preparing such the thixotropic polyurethane compositions.

It is known that polyurethane is superior in rubberlike elasticity, weather resistance, abrasion resistance and chemical resistance. For this reason polyurethane is widely used for various uses, for example, as an elastomer, a coating material, paint, sealant, waterproof filming agent, flooring material, wall material, synthetic leather and adhesive. In order to apply polyurethane to various objects for the above-mentioned purposes, a paste or liquid composition comprising a polyurethane prepolymer in a liquid phase or a solution of a polyurethane prepolymer is used. However, the conventional compositions for this purpose are of fluidity. Accordingly, if any of those compositions is applied to a vertical surface as a sealant or waterproof filming agent, it will flow down so that a good finishing cannot be expected. It is, therefore, required that the polyurethane prepolymer compositions have a good thixotropic property for a good workability.

In order to prepare a thixotropic polyurethane composition, an attempt was made to cause a polyurethanearea bridging utilizing both polyether glycol and diaminodiphenyl methane. Another attempt was made to add finely divided silica to a polyurethane prepolymer composition. Further, Japanese Pat. Publication No. 41, 110 of 1970 published December 23, 1970, discloses a thixotropic polyurethane composition which comprises a polyurethane prepolymer in a liquid phase or a solution of a polyurethane prepolymer, polyethylene glycol having an average molecular weight of 100 to 20,000 and colloidal silica. These known thixotropic polyurethane compositions are disadvantageous in that if they are prepared on an industrial scale, their quality is not uniform and that the polyurethane prepolymers obtained are unstable for storing and gelated for a short period. Particularly, the thixotropic polyurethane composition including polyethylene glycol having an average molecular weight of 100 to 20,000 as disclosed in Japanese Pat. Publication No. 41,110 of 1970 is inferior in the storing stability and causes an increase in hardness and a decrease in elasticity due to introduction of a single polyoxyethylene chain in addition to affection by terminal primary alcohol groups, with the result of this composition is not so good for use as thixotropic grouting material, waterproofing material and walling materials.

The primary object of the invention is, therefore, to provide an improved polyurethane composition having a good thixotropic property.

Another object of the invention is to provide a thixotropic polyurethane which has a good storage stability.

A further object of the invention is to provide a thixotropic polyurethane in which the disadvantages inherent to the conventional thixotropic polyurethane compositions can be avoided.

. A still further object of the invention is to provide an improved method for preparing a thixotropic polyurethane composition.

2 Other objects and advantages of the invention will become apparent from the following detailed description of the invention.

SUMMARY OF THE INVENTION According to the invention the improved thixotropic polyurethane composition comprises (a) a liquid of polyurethane prepolymer having at least two terminal free isocyanate groups and (b) a block polyether compound having at least two terminal secondary alcohol groups. The block polyether compound is a reaction product obtained by addition polymerization of ethylene oxide and propylene oxide in a block form to a starting material having two or three terminal active hydrogen groups in such a polymerization degree that the block polyether compound includes 30 to 409 moles of ethylene oxide and 3 to 172 moles of propylene oxide per molecule and the molar ratio between ethylene oxide and propylene oxide is within the range of 110.05 to 110.5.

The polyurethane prepolymer may be a reaction product obtained by addition polymerization of a polyisocyanate to an active hydrogen compound. Preferably, the polyurethane prepolymer has an average molecular weight within the range of 50 to 10,000. The liquid of a polyurethane prepolymer used in the invention may be either a polyurethane prepolymer in a liquid phase or a solution of a polyurethane prepolymer in an organic solvent.

In a preferred embodiment of the invention the polyurethane composition includes the above-mentioned block polyether compound in an amount of 0.01 to 50 parts by weight per parts of the polyurethane component of the prepolymer.

In a further preferable embodiment an inorganic material such as finely divided silica or bentonite may be added to the polyurethane composition to enhance its thixotropic property.

DETAILED DESCRIPTION OF THE INVENTION As described before, the thixotropic polyurethane composition according to the invention comprises a liquid or polyurethane prepolymer having at least two terminal free isocyanate groups and a block polyether compound having at least two terminal secondary alcohol groups. The polyurethane prepolymer having at least two terminal free isocyanate groups is a reaction product obtained by addition polymerization of a polyisocyanate to an active hydrogen compound.

The polyisocyanate which is one of the reactants for obtaining the polyurethane prepolymer is a compound having at least two NCO groups in one molecule. The polyisocyanate may be a member selected from the group consisting of 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, l-chlorophenylene-2,4-diisocyanate, 1.5-naphthalane diiso cyanate, 3,3 -bistoluene-4,4- diisocyanate, methylene bisphenylene-4,4-diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, polyaryl polyisocyanates, dimers and trimers of the foregoing and triisocyanates obtained by the reaction of one mole of a diisocyanate with three moles of a triol such as trimethylolpropane.

The active hydrogen compound to which the abovementioned polyisocyanate is added may be a member selected from the group consisting of polyols, amines, polyamines and the mixtures thereof and has two to six active hydrogen groups per moleculer and an average moleculer weight between 30 and 300 per said active hydrogen group. Preferably, the active hydrogen compound is a member selected from the group consisting of diand tri-ols of low molecular weights, such as ethylene glycol, 1,4-butandiol, glycerine, and trimethylol propane; polyalkylene glycols, such as polypropylene glycol and copolymers of ethylene oxide and propylene oxide; polymers obtained by the polymerization of a low moleculer weight triol, such as glycerine, trimethylol propane and 1, 2, 6-hexane triol, a low moleculer weight tetraol, such as pentaerythritol, or a low moleculer weight hexaol, such as sorbitol, with an alkylene oxide, such as ethylene oxide and propylene oxide; amines such as diethanol amine and triethanol amine; polyamines such as ethylenediamine and 4,4-methylene-bis-l-chloroanilene; and polymers obtained by the polymerization of one of said amines and polyamines with an alkylene oxide such as ethylene oxide and propylene oxide.

The polyurethane prepolymer thus obtained by addition polymerization of a polyisocyanate to an active hydrogen compound may preferably have an average moleculer weight within the range of 500 to 10,000.

The liquid of a polyurethane prepolymer may be either a polyurethane prepolymer in a liquid phase or a solution of a polyurethane prepolymer in an organic solvent. Among the preferred organic solvents there may be included esters such as ethyl acetate, butyl acetate and amyl acetate; ketones such as acetone, methyl ethyl ketone, diethyl ketone and methyl isobutyl ketone; aromatic hydrocarbones such as toluene, benzene and xylene; ethers such as tetrahydrofuran and dioxane; acid amide substitution compounds such as N,N- dimethyl formamide and N,N-dimethyl acetoamide; and dimethyl sulphoxide.

If polyurethane prepolymer is available in a liquid phase at the normal temperature, it may be used at it is. However, if polyurethane prepolymer is not available in a liquid phase, it is required to use an organic solvent to prepare a solution of polyurethane prepolymer. Acid amide substitution compounds such as N,N-dimethyl formamide and N,N'-dimethyl acetamide are most preferable for preparing a solution of polyurethane prepolymer.

ln order to provide a polyurethane composition with a good thixotropic property, the above-mentioned polyurethane prepolymer solution may preferably be prepared by diluting a polyurethane prepolymer with one of the above-mentioned organic solvents so that the polyurethane prepolymer content in the solution prepared is 25 to 40% by weight of the solution.

The other component of the thixotropic polyurethane composition according to the invention is a block polyether compound having at least two terminal secondary alcohol groups. The block polyether compound is a reaction product obtained by addition polymerization of ethylene oxide and propylene oxide in a block form to a starting material having two or three terminal active hydrogen groups. Addition polymerization of ethylene oxide and propylene oxide to the starting material should be carried out in such a polymerization degree that the obtained block polyether compound includes 30 to 409 moles of ethylene oxide and 3 to 172 moles of propylene oxide per molecule and the molar ratio between ethylene oxide and propylene oxide is within the range of 1:005 to 1:05.

The starting material may be a member selected from the groups consisting of diols, amines and triols of low 4 molecular weights such as ethylene glycol, propylene glycol, 1,4-butanediol, diethanoleamine, glycerine and trimethylol propane; polyalkylene glycols such as polyethylene glycol; and polyalkylene oxide such as ethylene oxide and propylene oxide.

Addition polymerization of ethylene oxide and propylene oxide to the starting material is carried out in a block form so that the reaction product has at least two terminal secondary alcohol groups. For example, addition polymerization of propylene oxide may be carried out after addition polymerization of ethylene oxide has been completed. Addition polymerization of propylene oxide to the starting material may also be carried out before and after addition polymerization of ethylene oxide. In any cases ethylene oxide and propylene oxide are polymerized in a block form so that the reaction product may have terminal secondary alcohol groups owing to addition polymerization of propylene oxide.

The ethylene oxide component in the block polyether compound should be 30 to 409 moles per molecule. The propylene oxide component in the block polyether compound should be 3 to 172 moles per molecule. The molar ratio between ethylene oxide and propylene oxide in the block polyether compound should be within the range of 120.05 to 110.5. In case where a compound which includes therein ethylene oxide and/or propylene oxide components, such as polyethylene glycol or an ethylene oxide-propylene oxide copolymer, is used as the starting material, the amounts of those ethylene oxide and/ or propylene oxide components initially included in the starting material should be taken into consideration to determine the amounts of ethylene oxide and propylene oxide components of the obtained block polyether compound.

The block polyether compound which is obtained by successive addition of ethylene oxide and propylene represented by the following formula:

CH3 cu wherein n is 30 to 409, m+m is 3 to 172 and n:(m+m') 110.05 to 110.5.

Although applicants do not wish to be bound by any theory of operation of the present invention, it is believed that various factors participate in providing the polyurethane composition according to the invention with a good thixotropic property and a good storage stability. Particularly, it is important that ethylene oxide and propylene oxide chains are polymerized in a block form in the polyether compound with the ethylene oxide and propylene oxide contents being within the before mentioned critical ranges, whereby the polyether compound includes both primary alcohol groups and secondary alcohol groups as terminal groups thereof, with the secondary alcohol group content being 40 to with respect to the total number of the terminal alcohol groups, in addition to the fact that propylene glycol groups are introduced to the compound.

The thixotropic polyurethane composition may be prepared by dissolving the block polyether compound in a liquid polyurethane prepolymer or an organic solvent solution of polyurethane prepolymer to form a mixture. In order to obtain a homogeneous mixture to provide the composition with a good thixogropic property, the mixing of the block polyether'compound with a liquid polyurethane prepolymer of a solution of poly urethane prepolymer may preferably be carried out at nate group content of 3.0% by weight was obtained. This prepolymer will be hereinafter referred to as Prepolymer A.

A mixture of 2,480g of polypropylene-ethylene glya temperature within the range of 60 to 120C and in col glycerol ether having an average moleculer weight an atmosphere of an inert gas such as nitrogen gas or of 5,000 with 620g of polypropylene glycol having an carbon dioxide gas. average molecular weight of 2,000 was reacted with In order to enhance the thixotropic property further- 460g of a tolylene diisocyanate mixture (comprising more and to more economically prepare the thixotro- 80% by weight of 2,4-tolylene diisocyanate and 20% by pie polyurethane composition, an inorganic material weight of 2,6-tolylene diisocyanate) in a nitrogen gas such as finely divided silica or bentonite be added flow atmosphere and at 120C for 3 hours. Another to the composition according to the invention. The colorless, transparent prepolymer having a terminal amount of the inorganic material added as a thixotropy free isocyanate group content of 3.6% by weight was enhancing agent should be within the range of 0.5 to 10 obtained. This prepolymer will be hereinafter referred parts by weight with respect to 100 parts by weight of to as Prepolymer B. polyurethane prepolymer included in the polyurethane To 100 parts of Prepolymer A or Prepolymer B varicomposition according to the invention. ous polyester compounds listed in Table l were added Preferably,the thixotropy enhancing inorganic matein the respectively indicated amounts. The mixtures rial is first added to a liquid polyurethane prepolymer were kneaded in a kneader at 80C and in a nitrogen or a solution of polyurethane prepolymer in an atmogas flow atmosphere for two hours to obtain pasty or sphere of an inert gas such as nitrogen gas or carbon digreasy compositions. oxide gas and at a temperature of 100+ to 150C to A slump test was carried out with respect to each of form a dispersion system. The block polyether comthe obtained compositions according to the slump test pound is then added to the dispersion system inthe method for silicone seatants defined in J1S-A-575 same inert gas atmosphere and at a temperature of 60 5-1969 (Japan Industrial Standard Test). The test reto 120C, taking about 5 to 10 minutes for mixing to sults are indicated in Table l in which found in thixform a homogeneous thixotropic polyurethane compootropy indicates for a slump test value of 0 to 1 mm sition. 7 while not found in thixotropy indicates for a slump test value of more than 1 mm. PREFERRED EMBODIMENT OF THE INVENTION Each of the above mentioned compositions was en- 2,540g of polypropylene glycol glycerol ether having closed with nitrogen gas in a 100 cc vessel and thermoan average molecular weight of 5,000 was reacted with stated at 0.5C in a sealing condition for days. 369 g of a tolylene diisocyanate mixture (comprising After then the appearance of each of the compositions by weight of 2,4-tolylene diisocyanate and 20% by was observed to determine the storage stability. The weight of 2,6-tolylene diisocyanate) in a nitrogen gas 35 test results are also indicated in Table 1 in which flow atmosphere and at 120C for 2 hours. To the reacgood in storage stability indicates no appreciable tion product liquid 640g of polypropylene glycol havchange in thixotropy or no gelation while no good in ing an average moleculer weight of 2,000 was added to storage stability indicates gelation or no thixotropy. carry out the reaction therebetween in a nitrogen gas Each of various polyester compounds listed in Table flow atmosphere and at 120C for 1 hour. A colorless, 40 1 has a CPR (Controlled Polymerization Rate) value of transparent prepolymer having a terminal free isocyaless than 10 measured by JlS-K1557.

Table 1 Sample Polyurethane Polyether Compounds Nos. Prepolymers Kinds Parts by Starting Ethylene Propylene Molar Parts by Type of Thixo- Storage Weight Materials Oxide Oxide Ratio of Weight Polymeritropy Stability (moles) (moles) EO/PO zation 1 A i 00 Ethylene 34 3 .5 1:0.1 10 Block Found Good glycol 2 A 100 Ethylene 45 3.5 1:0.08 10 Block Found Good glycol 3 A 100 Ethylene 68 6 .9 110.1 10 Block Found Good glycol 4 A 100 Ethylene 8 .6 120.1 10 Block Found Good glycol 5 A Ethylene 225 10 110.04 10 Block Found NO Good glycol 6 A 100 Ethylene 90 0 1:0 10 Found No Good glycol 7 B 100 Pro- 90 8.6 110.1 10 Block Found odnd pylene glycol 8 B 100 Pro- 90 0 1:0 l0 Found No Good pylene glycol 9 B 100 Glycerine 90 8 .6 1:01 10 Block Found Good 10 B 100 Glycerine 9O 1 .8 110.02 10 Random Not No Good Found 1 1 B 100 Glycerine 90 17.2 1:019 15 Block Found Good 12 B 100 Glycerine 90 68.8 l:0.8 15 Block Not No Good Found 13 B 100 Glycerine 450 0 1:0 10 Found No Good 14 B 100 Glycerine 408 34 .4 120.08 10 Block Found Good 15 B 100 Glycerine 225 172 1:013 15 Random Not No Good Found Table l-continued Sample Polyurethane Polyether Compounds Nos. Prepolymers Kinds Parts by Starting Ethylene Propylene Molar Parts by Type of Thixo- Storage Weight Materials Oxide Oxide Ratio of Weight Polymeritropy Stability (moles) (moles) EO/PO zation 16 A 100 Triethanol 90 172 l :O.l 10 Block Found Good amine 17 A 100 Triethanol- 450 110.04 l0 Block Found No Good amine 18 B lOO Triethanol- 90 8.6 l:O.l Block Found Good amine 19 B 100 Triethanol- 90 68.8 120.8 Block Not No Good amine Found 20 B 100 Triethanol- 225 172 l:O.8 15 Random Not No Good amine Found T0 100 parts of the before mentioned Prepolymer A or B various thixotropy enhancing inorganic materials listed in Table 2 were added in the respectively indicated amounts in a nitrogen atmosphere and at 100C to form a mixture. Each of the mixtures was kneaded in a kneader for one hour to form a homogeneous dispersion system. To the dispersion system after being cooled to 80C various polyester compounds listed in Table 2 were added. The mixtures were kneaded in a kneader at 80C and in a nitrogen gas flow atmosphere for 10 minutes to obtain pasty or greasy compositions. The slump and storage stability tests as mentioned before were conducted to determine the thixotropic property of each of the compositions. The test results thereof are indicated in Table 2.

Further, an rubber like elasticity test was conducted according to the vulcanized rubber property test defined in J lS-K-630l with respect to a hardened elastomer obtained by permitting each of the compositions to stand for seven days at room temperature. The test results thereof are also indicated in Table 2.

In Table 2, each of polyether compounds has a CPR value of less than 10 according to J IS-K-l557. Aerozeal No. 200 and Carplex No. used as thixotropy enhancing agents are SiO powder available from Japan Aerozeal Co., Ltd. and Shionogi Pharmaceutical Co., Ltd., both of Japan, respectively.

Table 2 Polyurethane Polyether Compounds Thixotropy Sample Prepolymers Enhancing Nos. Agents Nos. Agents Kinds Parts Starting Ethy- Pro- Molar Parts Type Kinds Parts Thixo- Storage y Materials lene pylene Ratio by of by tropy Stabili- Weight Oxide Oxide of Weight Poly- Weight ty (moles) .(moles) EO/PO merization 21 A 100 Ethylene 8.6 10 Block 0 Found Good 0.1 Glycol 22 A lOO 90 8.6 0.5 Aero- 3.5

zeal No. 200 23 A 90 8.6 2 Carp- 4 lex No. 80 24 A 100 Glycerine 90 l .8 l:- l0 Ran- Not No dom .02

Found Good 25 A 100 90 L8 l:- l0 Aero- 4 zeal No. 200 26 100 Ethylene 9O 0 1:0 10 Found Glycol 27 A I00 90 0 1:0 10 Aero- 5 zeal No. 200 28 B 100 Ethylene 90 8.6 10 Block 0 Found Good 0.1 Glycol 29 B 100 90 8.6 0.5 Aero- 3.5

zeal No. 200 30 B 100 Glycerine 90 8.6 l0 U (Ll 3] B 100 90 8.6 1.0 Curp- 5 Table 2-continued Polyurethane Polyether Compounds Thixotropy Sample Prepolymers E nhancing Nos. Agents Nos. Agents Kinds Parts Starting Ethy- Pro- Molar Parts Type Kinds Parts Thixo- Storage by M aterials lene pylene Ratio by of by tropy Stabili- Weight Oxide Oxide of Weight Poly- Weight ty (moles) (moles) EO/PO merization lex No. 80 32 B 100 90 68.8 l5 0 Not No Found Good 33 B 100 90 68.8 Aerol0 Found zeal No. 200 34 B 100 Ethylene 90 8.6 10 0 Good 0. l Glycol B 100 90 8.6 0.5 Carp- 3.5

[ex No. 80 36 A+B 50+50 Ethylene 90 8.6 10 Block 0 Found Good 0. I Glycol v 37 A+B 50+5O Ethylene 90 8.6 0.5 Block Aero- 3.5 Found Good 0. l Glycol zeal No. 200 38 A+B 50+50 90 8.6 1.0 Carp- 4 lex No. 80 39 A 100 Triethanol- 90 8.6 1.0 Block Aero- 3.5

0. l amine zeal No. 200 I B lOO 90 8.6 L0 3.5

Elastomer Sample Properties Nos.

Hard- Elon- Tensile ness gation Strength (Shore (Kg/cm) A 2 1 50 400 25 22 40 800 l 5 23 600 20 24 410 l 5 25 5 5 400 20 26 200 20 27 100 l 5 28 5 5 450 2 3 29 50 600 20 30 60 450 2 5 3 l 60 500 27 32 5 5 400 20 33 70 200 l 5 34 50 400 20 35 50 800 2 6 36 48 450 20 37 50 800 2 5 3 8 5 5 700 2 5 39 5 5 600 24 40 5 5 630 2 5 What is claimed is:

l. A thixotropic polyurethane composition comprising:

a. a liquid polyurethane prepolymer having at least 65 two terminal free isocyanate groups and an average molecular weight within the range of 50 to 10,000, said polyurethane prepolymer being obtained by the addition polymerization of a polyisocyanate with an active hydrogen compound, and b. a block polyether compound having both primary alcohol groups and secondary alcohol groups as terminal groups thereof, with the secondary alcohol number content being 40% to with respect to the total number of terminal alcohol groups, said 30 to 409 moles of ethylene oxide and 3 to 172 moles of propylene oxide per molecule and the molar ratio is within the range of 1 0.05 to 1 0.5.

2. A thixotropic polyurethane composition as defined in claim 1, in which said polyisocyanate is a member selected from the group consisting of 2,4-tolylene diisocyanate, 2,6-toly1ene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, l-chlorophenylene- 2,4-diisocyanate, 1.5-naphthalane diisocyanate, 3,3- bistoluene-4,4-diisocyanate, methylene bisphenylene- 4,4'-diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, polyaryl polyisocyanates, dimers and trimers of the foregoing and triisocyanates obtained by the reaction of 1 mole of a diisocyanate with 3 moles of trimethylolpropane.

3. A thixotropic polyurethane composition as defined in claim 1, in which said active hydrogen compound is a member selected from the group consisting of polyols, amines, polyamines and the mixtures thereof and has 2 to 6 active hydrogen groups per molecule and an average molecular weight between 30 and 300 per said active hydrogen group.

4. A thixotropic polyurethane composition as defined in claim 3, in which said active hydrogen compound is a member selected from the group consisting of diand tri-ols of low molecular weights, selected from the group consisting of ethylene glycol, 1,4-butandiol, glycerine, and trimethylol propane; polyalkylene glycols, selected from the group consisting of polypropylene glycol and copolymers of ethylene oxide and propylene oxide; polymers obtained by the polymerization of a low molecular weight triol, selected from the group consisting of glycerine, trimethylol propane and 1,2,6- hexane triol, a low molecular weight tetraol, selected from the group consisting of pentaerythritol, or a low molecular weight hexaol, selected from the group consisting of sorbitol, with an alkylene oxide, selected from the group consisting of ethylene oxide and propylene oxide; amines selected from the group consisting of diethanol amine and triethanol amine; polyamines selected from the group consisting of ethylenediamine and 4,4'-methylenebis-l-chloroamiline; and polymers obtained by the polymerization of one of said amines and polyamines with an alkylene oxide selected from the group consisting of ethylene oxide and propylene oxide.

5. A thixotropic polyurethane composition as defined in claim 1, in which said polyurethane prepolymer has an average molecular weight within the range of 500 to 10,000.

6. A thixotropic polyurethane composition as defined in claim 1, in which said liquid polyurethane prepolymer is a polyurethane prepolymer in a liquid phase.

7. A thixotropic polyurethane composition as defined in claim 1, in which said block polyether is included in said composition in an amount of 0.01 to 50 parts by weight per parts of the polyurethane.

8. A thixotropic polyurethane composition as defined in claim 1, further including an inorganic material for enhancing the thixotropic property, selected from the group consisting of finely divided silica and bentonite.

9. A thixotropic polyurethane composition as defined in claim 8, in which the amount of said inorganic material is 0.5 to 10 parts by weight with respect to 100 parts by weight of said polyurethane prepolymer included in said polyurethane composition.

10. A method for the preparation of a thixotropic polyurethane composition as defined in claim 1 which comprises mixing said block polyether compound with said liquid polyurethane prepolymer in an inert gas atmosphere and at a temperature within the range of 60 to C to form a homogeneous composition system.

11. A method for the preparation of the thixotropic polyurethane composition as defined in claim 8 which comprises the steps of adding said thixotropy enhancing inorganic material to said liquid of polyurethane prepolymer in an inert gas atmosphere and at a temper- 120C to form a homogeneous composition system. 

1. A THIXOTROPIC POLYURETHANE COMPOSITION COMPRISING: A. A LIQUID POLYURETHANE OREPOLYMER HAVING AT LEAST TWO TERMINAL FREE ISOCYANATE GROUPS AND AN AVERAGE MOLECULAR WEIGHT WITHIN THE RANGE OF 50 TO 10,000 SAID POLYURETHANE PREPOLYMER BEING OBTAINED BY THE ADDITION POLYMERIZATION OF A POLYISOCYANATE WITH AN ACTIVE HYDROGEN COMPOUND, AND B. A BLOCK POLYETHER COMPOUND HAVING BOTH PRIMARY ALCOHOL GROUPS, AND SECONDARY ALCOHOL GROUPS AS TERMINAL GROUPS THEREOF, WITH THE SECONDARY ALCOHOL NUMBER CONTENT BEING 40% TO 85% WITH RESPECT TO THE TOTAL NUMBER OF TERMINAL ALCOHOL GROUPS, SAID BLOCK POLYETHER COMPOUND BEING A REACTION PRODUCT OBTAINED BY ADDITION POLYMERIZATION OF ETHYLENE OXIDE AND PROPYLENE OXIDE IN BLOCK FORM TO A STARTING MATERIAL HAVING TWO OR THREE TERMINAL ACTIVE HYDROGEN GROUPS IN SUCH A POLYMERIZATION DEGREE THAT SAID BLOCK POLYESTER COMPOUND INCLUDES 30 TO 409 MOLES OF ETHYLENE OXIDE AND 3 TO 172 MOLES OF PROPYLENE OXIDE PER MOLECULE AND THE MOLAR RATIO IS WITHIN THE RANGE OF 1 0.05 TO 1 : 0.5.
 2. A thixotropic polyurethane composition as defined in claim 1, in which said polyisocyanate is a member selected from the group consisting of 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 1-chlorophenylene-2,4-diisocyanate, 1.5-naphthalane diisocyanate, 3,3-bistoluene-4,4''-diisocyanate, methylene bisphenylene-4,4''-diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, polyaryl polyisocyanates, dimers and trimers of the foregoing and triisocyanates obtained by the reaction of 1 mole of a diisocyanate with 3 moles of trimethylolpropane.
 3. A thixotropic polyurethane composition as defined in claim 1, in which said active hydrogen compound is a member selected from the group consisting of polyols, amines, polyamines and the mixtures thereof and has 2 to 6 active hydrogen groups per molecule and an average molecular weight between 30 and 300 per said active hydrogen group.
 4. A thixotropic polyurethane composition as defined in claim 3, in which said active hydrogen compound is a member selected from the group consisting of di- and tri-ols of low molecular weights, selected from the group consisting of ethylene glycol, 1,4-butandiol, glycerine, and trimethylol propane; polyalkylene glycols, selected from the group consisting of polypropylene glycol and copolymers of ethylene oxide and propylene oxide; polymers obtained by the polymerization of a low molecular weight triol, selected from the group consisting of glycerine, trimethylol propane and 1,2,6-hexane triol, a low molecular weight tetraol, selected from the group consisting of pentaerythritol, or a low molecular weight hexaol, selected from the group consisting of sorbitol, with an alkylene oxide, selected from the group consisting of ethylene oxide and propylene oxide; amines selected from the group consisting of diethanol amine and triethanol amine; polyamines selected from the group consisting of ethylenediamine and 4,4''-methylene-bis-1-chloroamiline; and polymers obtained by the polymerization of one of said amines and polyamines with an alkylene oxide selected from the group consisting of ethylene oxide and propylene oxide.
 5. A thixotropic polyurethane composition as defined in claim 1, in which said polyurethane prepolymer has an average molecular weight within the range of 500 to 10,000.
 6. A thixotropic polyurethane composition as defined in claim 1, in which said liquid polyurethane prepolymer is a polyurethane prepolymer in a liquid phase.
 7. A thixotropic polyurethane composition as defined in claim 1, in which said block polyether is included in said composition in an amount of 0.01 to 50 parts by weight per 100 parts of the polyurethane.
 8. A thixotropic polyurethane composition as defined in claim 1, further including an inorganic material for enhancing the thixotropic property, selected from the group consisting of finely divided silica and bentonite.
 9. A thixotropic polyurethane composition as defined in claim 8, in which the amount of said inorganic material is 0.5 to 10 parts by weight with respect to 100 parts by weight of said polyurethane prepolymer included in said polyurethane composition.
 10. A method for the preparation of a thixotropic polyurethane composition as defined in claim 1 which comprises mixing said block polyether compound with said liquid polyurethane prepolymer in an inert gas atmosphere and at a temperature within the range of 60* to 120*C to form a homogeneous composition system.
 11. A method for the preparation of the thixotropic polyUrethane composition as defined in claim 8 which comprises the steps of adding said thixotropy enhancing inorganic material to said liquid of polyurethane prepolymer in an inert gas atmosphere and at a temperature within the range of 100* to 150*C to form a dispersion system, and mixing said block polyether compound with said dispersion system in an inert gas atmosphere and at a temperature within the range of 60* to 120*C to form a homogeneous composition system. 